ABSTRACT Kentucky's high radon potential and high smoking rates create the perfect storm for the overrepresentation of lung cancer cases. Our transdisciplinary, community-academic team-led project, Radon on the RADAR (Residents Acting to Detect and Alleviate Radon) will address community concerns about lung cancer by identifying geological and atmospheric conditions that increase radon intrusion into homes, translating this knowledge into greater residential awareness of risk, enabling home radon testing and report back, and growing access to affordable and adequate radon mitigation. We will team geologists with citizen scientists to determine how new radon detection technology (i.e., Airthings) compares to traditional charcoal kits and outdoor soil radon measurements over a range of atmospheric and geological conditions to close a critical knowledge gap in our understanding of radon risk. The study will build capacity in environmental health by: (a) training citizens in rigorous data collection and interpretation of findings; (b) engaging these citizen scientists in creating and promoting library loan programs to increase radon testing; and (c) creating sustainable environmental health action plans to alleviate radon exposure in rural communities. Our overall hypothesis is that by increasing knowledge on how geological and atmospheric conditions can impact radon, partnering with citizen scientists to use new radon detection technology and translate the data, and by growing access to low-cost radon mitigation, we will reduce radon risk. Aim 1 will use a citizen science approach to identify and train 60 community residents in four KY counties to test for radon and evaluate change in environmental health literacy (EHL) and self-efficacy. Aim 2 will compare indoor home radon values and soil radon values over time, controlling for atmospheric conditions, seasonality, geology, topography, and smoking in the home. Aim 3 will create and evaluate a pilot radon detector library loan program with 400 homeowners in the four counties. Aim 4 will launch the radon detector loan program and examine changes in home testing and accessing geologically based radon potential maps. Aim 5 will examine the impact of citizen scientist-led radon coalitions on reach, effectiveness, adoption, implementation, maintenance, and environmental health literacy. The RADAR study challenges and expands the current environmental health science paradigm by collaborating with geologists and integrating their scientific approach. We will impact community concerns about high lung cancer rates by: 1) transforming radon detection and report back using geoscience and new radon gas detection technology; 2) developing a library-lending approach to increase radon testing; and 3) supporting environmental action by creating and sustaining citizen science-led radon coalitions that share new knowledge and engage health advocates, radon mitigation professionals, policymakers, builders, and developers to promote improved radon management in rural Kentucky.